Yarn winding



Feb. 12, 1957 s. A. PETERSEN 2,781,177

YARN WINDING Filed Feb. 5, 1953 2 Sheets-Sheet l J ':l 7 l g l i i l I I I .122: 2:: :s'

37 if 48 'i INVENTOR.

SVEND A. PETERSEN ATTORNEYS.

Feb. 12, 1957 s, A. PETERSEN 2,781,177

YARN WINDING Filed Feb. 5, 1953 2 Sheets-Sheet 2 38 INVENTOR.

SVEND A; PETERSEN Q TORNEYS.

Unite States Patent YARN WINDING Svend A. Petersen, Brooklyn, N. Y., assignor to Celanese Corporation of America, New York, N. Y., a corporation of Delaware Application February 5, 1953, Serial No. 335,226

11 Claims. (Cl. 242-18) This invention relates to a yarn winder and relates more particularly to a horizontal yarn winder and to a damping mechanism employed therein.

For the winding of yarn packages such as cheeses and the like, it is the general practice in the textile industry to employ a so-called horizontal winder. This winder comprises a supporting arm that is pivotally mounted at one point and carries, at a point spaced from its mounting, a suitable freely rotatable mandrel for engaging a yarn package. There is also provided in said winder a positively driven roll whose axis lies parallel to the axis of the mandrel and against which the yarn package bears. The rotation of the positively driven roll drives the yarn package through friction at a constant peripheral speed to wind the yarn thereon at a constant linear rate. The yarn is distributed axially along the package being formed by the winding operation in any desired manner by means of a suitable'traverse mechanism that guides the yarn onto the yarn package.

The winding of the yarn onto the yarn package is carried out at speeds of up to 1000 meters per minute or more, and at rotational speeds of up to 4400 revolutions per minute or more. When, at these speeds, the yarn windings on the package depart from a circular crosssection as, for example, by developing a high spot, there is tendency for the yarn package to bounce away from the drive roll. As a result, the pressure between the yarn package and the drive roll will fluctuate thereby introducing further irregularities into the yarn windings. The tendency of the yarn package to bounce away from the drive roll not only results in the production of irregular packages, but also acts to limit the maximum speed at which the horizontal winder can be operated.

It is an important object of this invention to provide a yarn winder which will be free from the foregoing and other disadvantages and which will be especially simple in construction and efiicient in operation.

A further object of this invention is to provide in a horizontal yarn winder a hydraulic damping mechanism for maintaining a uniform pressure between the yarn package and the drive roll.

Another object of this invention is to provide an improved hydraulic darnping mechanism.

Other objects of this invention, together with certain details of construction and combinations of parts, will be apparent from the following detailed description and claims.

According to the present invention, there is provided a yarn winder comprising a movable supporting arm that carries a freely rotatable mandrel for engaging a yarn package. The yarn winder also includes a positively driven roll which is in frictional engagement with the yarn package and serves to drive the same at a constant peripheral speed. The movable supporting arm is operatively connected to a hydraulic damper which will interpose little or no resistance to slow movements of the supporting arm, but which will interpose a considerable resistance to rapid movements of said arm. Thus, as the LifiIIltI of the yarn package builds up there will be little or no resistance to the movement of the supporting arm necessary to permit the axis of the mandrel carrying the yarn package to move away from the drive roll. However, in the event that any irregularities develop in the yarn package which would tend to cause the yarn package and the supporting arm carrying the same to bounce, the hydraulic damper will impose a considerable resistance to such movement. As a result, the tendency of the yarn package to bounce will be substantially eliminated and, in addition, the pressures developed by the hydraulic damper between the drive roll and the yarn package will tend, upon the addition of further windings to the package, to restore the said package to a truly circular cross-section.

When the yarn package is'filled, the mandrell carrying said package is moved away from the drive roll to break the frictional contact between the yarn package and the drive roll. The yarn package is then doffed. T o eliminate the resistance by the hydraulic damper to the movement of the yarn package to the clotting position, means are provided for rendering said hydraulic damper substantially inoperative during such movement. Stop means are provided for definitely fixing the position of the yarn package during the dofling operation. To prevent the yarn package or the means carrying the same from striking the said stop means with sufiicient force to cause damage, the hydraulic damper may again be rendered operative immediately before the yarn package reaches the dofiing position so that the movement of said yarn package to said position will be cushioned. After the dofiing of the yarn package, the mandrel is moved to bring a new yarn package support into frictional contact with the drive roll for the winding of another yarn package. During such movement, means are provided for greatly reducing the resistance of the hydraulic damper so that said movement may be effected rapidly and without the use of excessive force.

In one form of apparatus for carrying out this invention, the mandrel is supported by an arm that is pivotally mounted at a point spaced from the mandrel. Connected to said arm, at the pivot point for rotation therewith, is a shaft which comprises a part of the hydraulic damper. The shaft extends through a liquid-tight chamber, of generally cylinrical form, which is filled with a liquid such as oil. The chamber is divided into two sections by means of a stationaryrectangular plate that extends from the walls of the chamber almost into contact with the shaft, and by a rectangular vane which is fastened to the shaft and extends almost into contact with the walls or" the chamber. The movement of the arm supporting the mandrel will cause the shaft and the vane fastened thereto to rotate in the oil-filled chamber forcing the oil in said chamber to flow through the clearance between the said vane and walls of the chamber. By selecting a suitable clearance between the vane and the walls of the chamber, the flow of oil through said clearance will impart the desired resistance to the movement of the arm. Because the clearance between the vane and the walls of the chamber through which the oil flows comprises a series of elongated rectangular apertures, it has been found that there is a higher resistance to the flow of oil therethrough than throughv a circular aperture having the same area as the total area of the rectangular apertures. As a result, when using elongated rectangular apertures it is possible to obtain the desired resistance to movement with apertures having a relatively large total area so that the clearances between the vane and the walls of the chamber may be made large enough to 7 present no problem for commercial production.

To render the hydraulic damper substantially inopera tive during the movement of'the yarn package to the doffing position, the oil-filled chamber may be given a non-circular contour over a' portion of its periphery so as greatly to increase the clearance between said vane and the walls of said chamber during such movement. The clearance between the vane and the walls of the chamber may be reduced again, immediately before the vane reaches a position corresponding to the doing position, so asto cushion the movement .of the yarn package to the doffing position. To reduce the resistance to the movement of the yarn package from the doffing position back to the winding position, a check valve may be provided which will permit the oil to flow from one section of the chamber to the other section. By regulating the loading on said check valve it is possible to impart any desired degree of resistance to the movement of the yarn package to the winding position.

A preferred embodiment of thisinventionis shown in the accompanying drawings wherein Fig. 1 is a front elevational view, partly in section, of a horizontal yarn winder including the hydraulic damper of this invention,

Fig. 2 is a cross-sectional view, taken-on the line 2-2 in Fig. 1, in the direction of thearrows,

Fig. 3 is a detail cross-sectional view, on an enlarged scale, of the hydraulic damper, taken on the line 33 in Fig. l, in the direction of the arrows, and

Fig. 4 is a detail cross-sectional view, of the pressure relief cylinder, taken on the line 4-4 in Fig. 3, in the direction of the arrows.

Referring now to the drawing, the reference numeral 11 designates a machine frame provided with a boss 12 in which is rotatably'journall'ed a shaft 13 driven by any suitable means (not shown). The shaft 13 carries a drive roll 14 which is adapted to frictionally engage the surface of a yarn package 15, mounted on a freely rotatable mandrel 16, for the purpose of rotating said yarn package.

While the mandrel 16 may be of any'suitable design, one

design that has been found highly satisfactory is that shown in S. A. Petersen and H. Chow application S. No.

335,013, filed February 4, 1953, now Patent No. 2,733,- 874, issued February 7, 1956. During the actual winding operation, the rotation of the drive roll 14 causes the yarn package 15 to rotate, drawing a yarn 17 from any suitable source (not shown) onto the said yarn package through a yard guide 18 which is traversed by any suit-- trical conductors to drain any static charges that may ac-- cumulate on the surface of the roll14.

' The mandrel 16 is supported for free rotation on a shaft 23 fastened to an arm 24 that is pivotally mounted at its lower end between a fitting, indicated generally by reference numeral 25, and a hydraulic damper, indicated generally by reference numeral 26. The pivotal mounting of the arm 24 permits the mandrel 16 carrying the yarn package 15 to be moved away from the drive roll: 14 as the diameter of the yarn winding on said yarnpackage increase and to be moved entirely clear of the drive roll 14 for dotting and donning the yarn package 15 Pivotally fastened to the upper end of the arm,24 by means of a pin 27 is a handle 28 which can be used to rotate the arm 24 so as to bring the yarn package 15 into contact with the drive roll 14 or to move it away' from said drive roll. At its lower end, the handle 28 is provided with a projection 29 which will function to brake the rotation of the mandrel 16 when the handle 28 is pivoted about the pin 27 as morefully described .in the Petersen et a1. application referred to above.

A stop 31provided on the arm 24'acts to limit the return movement of the handle 28fand projection 29 with respect to the mandrel'lfi. The arm 24 is provided at its lower end with a lip 32 which abuts against a stop 33 projecting from the machine frame 11 when the arm 24 is rotated to the extreme right as shown in dotted lines 24" in Fig. 2 of the drawings to limit the maximum movement of the said arm in the-directionaway from the roll 14.

The fitting comprises an aperturedrib-34 on the machine frame 11 and a screw 35 .threaded through; the aperture in said ribfThe screw 35 is provided with a tapered end 36 that fits into a tapered seat 36 in the arm 34 to provide one support forsaid arm. The hydraulic damper; 26 comprises a, damper: assembly, indicated generally by reference numeral 37 and which will be described below, having a shaft 38 projecting therefrom and received in a bore 39 extending through the arm 24. The shaft 38 is fastened'to the arm 24'by means of a set screw 41 so that the shaft and arm will turn as a unit. As another supportfor the arm 24 thereis provided anannular'collar. 42 concentric with the shaft 33 and positioned between the damper assembly 37 and the arm 24. The internal diameter of the annular collarv 42 is greater than the external diameter of the shaft-381 so thatsaid shaft may rotate freely in said collar. The annular. collar-42 .is provided with a tapered end 43 that fits vinto a tapered seat 44 in the arm-24 to provide a secondsupport for said arm. A proper fit maybe obtained between the tapered ends 36 and 43- and' the: tapered seats 36? and44, respectively, and any play or wear 'between said members may be readily corrected, byadjustingthe position of the screw 35,-:which, once-adjusted, may be held securely in-placeby means of ascrew 45.

which is ada'ptedto clamp split ends 46 of the apertured rib'34to prevent movementofthe saidscrew 35,

Thedamper assembly 37 comprises a cylindrical mem-,

ber, 47. having an open. endadapted. to. be closechbjy a 47 and cover 48 to form a liquid tight'chamber 51;. The

chamber 51 may be filled with oil supplied through apetcock 52.. The shaft 38 extends through the center of the chamber. 51, being journalled for rotation in themember 47 and the cover 48, and being provided with spaced.

grooves 53 extending around its periphery. The grooves 53 are adapted to receivev suitable packing material, as

shownat 54, to prevent the leakage of oil from said cham:.

inplace by means of screws'58 that extend through the, 'walls of the chamber 51.

One end of stationary plate 57 is in contact with the inner wall of the chamber 51 and is slightly spaced from theshaft 38, the construction of said. stationary plate being such that it acts, together.

with the vane 56, to divide thechamber 5 1 intotwosections.. When the winding. of a yarn package 15. is. to

be in, the center line of. the arm 24 will be in the position shown by broken line 24? (Fig. 2'), with the empty yarn package support. 15 hearing against the drive. roll 14. At thistime, the vane 56 will be in-the po sition 56' shown in 'Fig. 3 of the drawings. wound onto the yarn package 15, the diameter of the said yarn package 15 will gradually increase thereby.

causing. the arm. 24 to rotate about its pivotal supports in a clockwise direction as viewed in Fig. 2 ofthe draw- The rotation of the arm. 24 will cause the shaft 38 direction. During the slow rotation of the shaft 38 and the vane 56 caused. by the. increase in the diameter of the yarn package 15, the, oilin the chamber 51 will flow past the clearance formed between the. vane. 56 and. the.

As the yarn 17. is.

walls of said chamber without imposing any considerable resistance to the movement of said shaft 38. If, however, any high spots or other irregularities should develop in the winding of the yarn package 15 which would tend to cause the said yarn package 15 to bounce away from the drive roll, there will be a tendency for the arm 24, and the shaft 38 on the vane 56 secured thereto to move with a sudden, jerky movement. The resistance to the flow of oil through the clearance between the vane 56 and the wall of the chamber 51 will efiectively prevent such sudden, jerky movements and, upon addition of further winding to the yarn package, will also tend to eliminate the high spots or other irregularities from the yarn package 15 and restore said yarn package to a truly circular cross-section.

When the winding of a yarn package 15 is complete, the said yarn package will have a diameter as shown by 15 (Fig. 2), the center line of the arm 24 will have moved to the position 24" and the vane 56 will have moved to the position shown in full lines in Fig. 3 of the drawing. At this time the operator, in order to move the yarn package 15 away from the drive roll to a dofiing position, will grasp the handle 28 and move the arm 24 in a clockwise direction, as viewed in Fig. 2 of the drawings. To eliminate the resistance to such movement which would exist if it were necessary to force the oil in the chamber 51 through the small clearance between the vane 56 and the wall of the chamber 51, the chamber '51 is given a non-circular contour at 59 to increase the clearance between the vane 56 and the wall of the chamber 51. As a result, there will be relatively little resistance to the movement by the operator of the arm 24 to the dofiing position. However, to prevent the lip 32 from striking the stop 33 with sufiicient force to damage one or both of said elements, the clearance between the vane 56 and the wall of the chamber 51 is reduced so that there is again a considerable resistance to the movement of the arm 24 immediately prior to the contact between the lip 32 and the stop 33. Through this design, the arm 24 will move slowly to its dofiing position 24" (Fig. 2) at which point the vane 56 will be in the position 56" (Fig. 3).

The plate 57 is provided with a spring-loaded checkvalve 61 which will open to permit oil to flow from one side of said plate to the other side of said plate if the pressure developed in the chamber 51 at any time during the movement of the vane 56 from the starting to the dotting position should become excessive.

After the dofi'ing of the yarn package 15, a fresh yarn package support is placed on the mandrel 16 and the operator moves the arm 24 back to the starting position to begin the winding of another yarn package 15. To permit said movement to be made quickly and without the use of excessive force, the vane 56 is provided with a spring-loaded check-valve 62 which will permit oil to fiow from one side of said vane to the other side of said vane when the pressure in the chamber 51 developed by said movement exceeds a predetermined value. Through the presence of the spring-loaded valve 62, the force necessary to move the arm 24 to the starting position can be kept low. Yet by properly selecting the loading spring of said valve 2 sufficient resistance to said movement may be developed to prevent the yarn package 15 from coming into contact with the drive roll 14 with a force so great as to damage one or both of said members.

For best results, it is desirable that the chamber 51 be completely tilled with oil at all times. One technique, that has been highly successful in elfecting such complete filling, is to enter the oil into the chamber 51 at a temperature below normal so that as the oil warms to normal temperature it will expand and develop a pressure in said chamber. To prevent the pressure in the interior of the chamber 51 from becoming excessive through the expansion of the oil caused by the heat generated during operation, there is provided in the closed end of the member 47, a piston 63 which rides in a bore 64 and is urged into the chamber 51 by a spring 65. Actual entry of the piston 63 into the chamber 51 is prevented by the plate 57 which overlies a portion of the bore 64 and acts as a stop. When the pressure of oil in the chamber 51 increases, the piston 63 will be forced into the bore 64 against the action of the spring 65, permitting the oil to expand, while when the pressure of oil in the chamber 51 decreases the spring 65 will force the piston 63 outwardly in the bore 64 returning the oil to the chamber 51 proper. To prevent leakage of oil, the piston 63 is provided around its periphery with a groove 66 in which is positioned packing material 67.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of my invention.

Having described my invention what I desire to secure by Letters Patent is:

1. A winder for yarns comprising a rotatable mandrel for supporting a yarn package, a drive rollfor driving the yarn package through frictional contact with the surface of the yarn package, a damper operatively connected to the mandrel for interposing a resistance to movements of said mandrel, said mandrel being moveable from winding position with the yarn package in contact with the drive roll to a doffing position with the yarn package out of contact with the drive roll, and means for reducing the resistance by the damper to the movement of the mandrel during at least a portion of the movement of the mandrel from the winding to the dofiing position.

2. A winder for yarns comprising a rotatable mandrel for supporting a yarn package, a drive roll for driving the yarn package through frictional contact with the surface of the yarn package, a damper operatively connected to the mandrel for interp-osing a resistance to movements of said mandrel, said mandrel being moveable from a winding position with the yarn package in contact with the drive roll to a dofling position with the yarn package out of contact with the drive roll, means for reducing the resistance by the damper to the movement of the mandrel during at least a portion of the movement of the mandrel from the winding to 'the doffing position, and means for increasing the resistance by the damper to the movement of the mandrel immediately prior to the movement of the mandrel into the dofling position to cushion the movement of the mandrel into the dofling position.

3. A winder for yarns comprising a pivotally mounted arm, a rotatable mandrel for supporting a yarn package fastened to said arm at a position spaced from the pivot point, a drive roll for driving the yarn package through frictional contact with the surface of the yarn package, a

hydraulic damper operatively connected to the arm for interposing a resistance to movements of said arm, said arm being movable from a winding position with the yarn package in contact with the drive roll to a doffing position with the yarn package out of contact with the drive roll, and means for reducing the resistance by the hydraulic damper to the movement of the arm during at least a portion of the movement of the arm from the winding to the doffing position.

4. A winder for yarns comprising a pivotally mounted arm, 'a rotatable mandrel for supporting a yarn package fastened to said arm at a position spaced from the pivot point, a drive roll for driving the yarn package through frictional contact with the urface of the yarn package, a hydraulic damper operatively connected to the arm for interposing a resistance to movements of said arm, said arm being moveable from a winding position with the yarn package in contact with the drive roll to a dofiing position with the yarn package out of contact with the drive roll, means for reducing the resistance by the hydraulic damper to the movement of the arm during at least a portion of the movement of the arm from the 5. A winder for yarns comprising a pivotally mounted arm, a rotatable mandrel for supporting a yarn package fastened to said arm at a position spaced from the pivot point, a'drive roll for driving the yarn package through rictional contact with the surface of the yarn package, a hydraulic damper operatively connccted'to the arm for interposing a resistance to movements of said arm, said arm being moveable from a Winding position with the yarn'package in contact with the drive roll to a dotfing position with the yarn package but of contact with the drive roll, means for reducing the resistance by the hydraulic damper to the movement of the arm'during at least a portion of the movement of the arm from the Winding to the'dofiing position, means for increasing the resistance by the hydraulic damper to the movement of the arm immediately prior to the movement of the arm into the dofiing position, and means reducing the resistance by the hydraulic damper to the movement of the arm from the doflin g position'to the winding position.

6. A winder for yarns comprising a pivotally mounted arm, a rotatable mandrel for supporting a yarn package fastened to said arm at a position spaced from the pivot point, a drive roll for driving the yarn package through frictional contact with the surface of the yarn package, a chamber having a liquid therein, a vane positioned in said chamber andspaced from the wall of said chamber.

to form an aperture through which the liquid in the chamber can how on movement of the vane, means operatively connecting the arm to the vane whereby movements of the arm will cause movements of the vane and thereby interpose a resistance to the movement of the arm, said arm being nioveable from a winding position with the yarn package in contact with the drive roll to a dofling position with the yarn package out of contact with the drive roll, and said chamber being contoured to provide an increased clearance between the vane and the wall of the c-hamber'during at least a portion of movement of the arm from the winding to the doffing position to decrease the resistance to the movement of the 'arm from the winding to the d'ofling position.

7. A winder for yarns comprising a pivotally mounted arm, a rotatable mandrel for supporting a yarn package fastened to said arm at a position spaced from the pivot point, a drive roll for driving the yarn package'through frictional contact with the surface of the yarn package, a chamber having a liquid therein, a vane positioned in said chamber and spaced from the Wall of said chamber to form an aperture through which the liquid in the chamber can flow on movement of the vane, means opera-tively connecting the arm to the vane whereby movements of the arm will cause movements of the vane and thereby interpose a resistance to the movement of the arm, said aim being moveable from a winding position with the yarn package in contact with the drive roll to a dotting position'with the yarn package out of contact with the drive roll, said chamber being contoured to provide an increased clearance between the vane and the wall or" the chamber during at least a portion of movement of the arm from the winding to the dotting position to decrease the resistance to the movement of the arm from the winding to the doihng position, and said chamher being contoured to provide a reduced clearance between the vane and wall of the chamber immediately prior to movement of the arm into the doffing position to cushion the movement of the arm into the doffing position.

8. A winder for yarns comprising a pivotally mounted arm, a rotatable mandrel for supporting a yarn package fastened to said arm at a position spaced from the pivot point, a drive roll for driving the yarn package through frictional contact with thesurfac'e of the yarn package, a chamber having a liquid therein, a vane positioned in said chamber and spaced from'the wall of said chamber to form'an aperture through'which the liquid'i'nthe chamber'can fiow on movement of the vane, means operatively connecting the arm to the vane whereby movements of the arm will cause movements of the vane and thereby interpose a resistance to the movement of the arm, said arm being nioveable from a winding position with the yarn package in contact with the drive roll to a doifing position with the yarn package out of contact with the drive roll and back again, and a check valve to permit liquid to flow from one side of said vane to the other side of saidvane when the'arm is moved from the dofiing posito the winding position to decrease the resistance to movement of the arm from the doffing position to the winding position.

9. A Winder for yarns comprising a 'pivotally mounted arm, a rotatable mandrel for supporting a yarn package fastened to said arm at a position spaced from the pivot point, a drive roll for driving the yarn package through frictional contact with the surface of the yarn package, a chamber having a liquid therein, a vane positioned in said chamber and spaced from the wall of smd chamber to form an aperture through which the liquid in the chamber can fiow on movement of the vane, means operatively connecting the arm to the vane whereby movements of the arm will cause movements of the vane and thereby interpose a resistance to the movement of the arm, said arm being moveable from a winding position with the yarn package in contact with the drive roll to a doting position with the yarn package out of contact with the drive roll and back again, s'aid chamber being contoured to provide an increased clearance between the vane and thewali of the chamber during at least a portion of movement of the arm from the winding to the dotting position to decrease the resistance to the movement of the arm from the Winding to the dotting position, and said chamber being contoured to provide a reduced clearance between the vane and wall ofthe chamber immediately prior to movement of the arm into the dotting position to cushion the movement of the arm into the dofiing position, and a check valve to permit liquid to flow from one side of said vane to the other side of said vane when the arm is moved from the dofiing position to the winding position to decrease the resistance to movement of the arm from the dotting position to the winding position.

10. A winder for yarns comprising a pivotally mounted arm, a rotatable mandrel for supporting a yarn package fastened to said arm at a position spaced from the pivot point, a drive roll for driving the yarn package through frictional contact with the surface of the yarn package, a liquid tight chamberof generally cylindrical form having a liquid therein, ashaft fastened to the arm for movement therewith and extending through said chamber, a stationary plate extending from said shaft into contact with the wall of thechamber, a rectangular vane fastened to said shaft and extending almost into contact with'the wall of the chamber to form an elongated aperture through which the liquid in the chamber can how on movement of the vane to i'nterpose a resistance to movement of the vane, said plateand said vane separating the chamber into t-Wosections, the arm being moveablefrom a winding position with the yarn package in contact with the drive roll to a doffin-g position with the yarn package out of contact with the drive roll and back again, said chamber being contoured to provide an increased clearance between the vane and the wall of the chamber during at least a portion of the movement of the arm from the Winding to the dofiing position to decrease the resistance to the movement of the arm from the winding to the doffing position, and said chamber being contoured to provide a reduced clearance between the vane and Wall of the chamber immediately prior to movement of the arminto the doffing position, acheck valve in saidvane to permit liquid to flow meme? from one side of said vane to the other side of said vane when the arm is moved from the doffing position to the winding position to decrease the resistance to movement of the arm from the dofiing position to the winding position, a check valve in said plate to permit liquid to flow from one side of said plate to the other side of said plate when the pressure on the liquid to one side of said plate exceeds a given value and a pressure relief comprising a spring loaded piston moveable in a cylinder opening into said chamber to compensate for fluctuations in the pressure of the liquid in the chamber.

11. A damper comprising a liquid tight chamber of generally cylindrical form having a liquid therein, a shaft extending through said chamber, a stationary plate extending from said shaft into contact with the wall of the chamber, a rotatable rectangular vane fastened to said shaft and having a longitudinal edge extending almost into contact with the Wall of the chamber to form an elongated aperture through which the liquid in the chamber can flow on angular movement of the vane to interpose a resistance to movement of the vane, said plate and said vane separating the chamber into two sections, said chamber being contoured to provide an increased clearance between an end of the vane and the wall of the chamber to decrease the resistance to the movement of said vane during a portion of said movement, and said chamber being contoured to provide a reduced clearance between the vane and wall of the chamber adjacent one limit of the movement of the vane to cushion the movement of the vane to said limit, a check valve in said vane to permit liquid to flow from one side of said vane to the other side of said vane when the vane is moved in a given direction to decrease the resistance to movement of the vane in said direction, a check valve in said plate to permit liquid to flow from one side of said plate to the other side of said plate when the pressure on the liquid to one side of said plate exceeds a given value, and a pressure relief comprising a spring loaded piston moveable in a cylinder opening into said chamber to compensate for fluctuations in the pressure of the liquid in the chamber.

References Cited in the file of this patent UNITED STATES PATENTS 913,349 Batault et al Feb. 23, 1909 1,176,014 Wyeth et a1 Mar. 21, 1916 1,825,233 Joyce Sept. 29, 1931 2,060,804 Friestedt Nov. 17, 1936 2,070,413 Sandberg Feb. 9, 1937 2,193,738 Perrin Mar. 12, 1940 2,286,516 Swanson June 16, 1942 2,466,109 Jencks Apr. 5, 1949 FOREIGN PATENTS 399,700 France Apr. 29, 1909 484,489 France July 17, 1917 473,121 Great Britain Oct. 6, 1937 530,811 Great Britain Dec. 20, 1940 

